DONETSK, Ukraine — Almost two weeks after Malaysia Airlines Flight 17 was blown out of the sky, the remains of some passengers are feared rotting in the 90-degree midsummer heat, deepening the frustration of relatives desperate to recover the bodies of their loved ones.

Fighting between Ukrainian forces and separatist rebels has kept away international police charged with securing the site, a sprawling area of farmland and villages.

Until it’s secured, there is no way for forensic experts to gather remaining bodies or collect debris for analysis.

Even the rebels — who initially oversaw the collection of more than 200 of the 298 bodies in a disorganized, widely criticized effort — have stopped their work, saying attacks from the Ukrainian military have forced them to focus on defending themselves.

It remains unclear how many bodies remain and what condition they are in after being exposed for so long to the elements. Dutch officials are adamant there are still bodies to be recovered, and Prime Minister Mark Rutte has said repeatedly that bringing them back is his government’s top priority.

But Dutch officials were gloomy Wednesday about the prospects of reaching the site soon.

“We don’t expect the security situation to improve enough over the next few days to make this possible,” said Pieter-Jaap Aalbersberg, head of the Dutch-led recovery mission.

Two crucial pieces of evidence, the flight recorders, have been retrieved and analyzed.

The U.S. and Ukrainian governments say the Boeing 777 was brought down July 17 by a Russian-made missile fired by eastern Ukraine’s pro-Moscow separatists. The separatists deny it. Russia denies providing the Buk missile launcher and says the Ukrainian military may have shot the plane down.

After the investigative team’s failure to reach the site Wednesday, the United Nations called on both sides in Ukraine’s grinding civil conflict to cease hostilities in the area.

“The families of the victims of this horrific tragedy deserve closure, and the world demands answers,” U.N. spokesman Stephane Dujarric said.

In their latest attempt to get to the wreckage zone, observers from the Organization for Security and Cooperation in Europe left in two vehicles from the rebel-held city of Donetsk but got only as far as the city’s outskirts. The observers talked with rebels and turned back after being “warned of gunfire on the route and in the surrounding areas,” the Dutch said in a statement.

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